Detection of Water on Comets

As we have already pointed out, comets may have been very important for the Earth and terrestrial planets because they deposited during collisions considerable amounts of water on the surfaces of these planets. On March 18, 1988 dark features on nine consecutive photographs were observed on Venus. Since film defects and other interferences (e.g. from an artificial Earth satellite or interplanetary object) can be ruled out, it is highly probable that this event was an impact of a small cometary like object that took place on the upper haze layer of the dense Venusian atmosphere. Because such an object consists mainly of water, evaporation of H2SO4 particles occurred which decreased the albedo at the point of entrance and therefore a dark feature appeared (Kolovos, Varvoglis and Pylarinou, 1991 [189]). 

Water has strong absorption bands around 1.45,1.95 and 2.50 pm. Mumma et al. 1986 [241] reported on the detection of water vapor in Halley s comet. Nine spectral lines around 2.65 pm were found by means of a Fourier transform spectrometer on the NASA-Kuiper Airborne Observatory. The water production rate was about 6 X 10 molecules per second on 22.1 December and 1.7 x 10 molecules per second on 24.1 December UT in 1985. 

Ground based detection of gaseous water in the coma of comet Halley was reported by Knacke et al., 1986 [185]. They observed at 1.4 and 1.9 pm and derived a mass loss rate from the intensities observed of 2 x 10 molecules/s. The detection of water group ions from comet Halley by means of Sakigake was described by Oyama and Abe, 1990 [257]. During the impact of Shoemaker Levy on Jupiter, water was detected in the resulting fireball of the fragments G and K (Bjoraker et al., 1994 [31] and 1996 [32]). 

Davies et al., 1997 [96] investigated spectra of Comet Hale-Bopp (C/1995 Ol) covering the range 1.4-2.5 pm that were recorded when the comet was 7 AU from the Sun and they found broad absorption features at 1.5 and 2.05 pm. Much of the light from the comet is scattered from the coma, some of the absorption features can be matched by an intimate mixture of water ice and a low-albedo material such as carbon on the nucleus. Furthermore, the absence of the 1.65 pm absorption feature of crystalline ice suggests that the cometary ice was probably in an amorphous state at the time of these observations. 

Comsovici et al., 1998 [78] observed Comet Hyakutake C/1996 B2 during the period 26 Aprils May 1996 around perihelion searching for the 22 GHz neutral water line by using a fast multichannel spectrometer coupled to the 32 m dish of the 

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